Unmanned aircraft or spacecraft (in the following, this term is used synonymously with the abbreviation RPA) are being used to an increasing extent for transporting loads, for surveillance or reconnaissance missions or also for military tasks. Many people also consider such an option as the future for passenger transportation. However, an aircraft can also be controlled by one or more pilots who, for various reasons, may be unavailable in any case for a particular period of time, which is why the wording “at least temporarily unmanned” has been chosen. Of course, conceptually, “unmanned” only means occupation of the cockpit; irrespective of this, people may or may not be on board the aircraft, whose presence or absence, however, does not affect the control.
The aircraft or spacecraft concerned usually flies through an airspace monitored by intercommunicating stations of the air traffic control (ATC) in accordance with a flight plan which has to be submitted and approved before the flight procedure commences. The only real difference between an unmanned flight procedure and a manned flight procedure can be considered to be that a pilot who is responsible for, and has discretionary control over, flight movements and the changes thereto (known as PIC, pilot in command or also PIL, pilot in the loop) is not simultaneously present in the aircraft or spacecraft, but gives control commands and (co)monitors systems of the aircraft or spacecraft at another location, or what is referred to as an RPS (remote pilot station).
The ability or possibility of influencing the behavior of the aircraft or spacecraft during the flight is provided by a C2 (command & control) link system which establishes various control and communication capabilities. The D2 data link can be realized by a LOS (line of sight) link or by a BLOS (beyond line of sight, i.e., satellite) link, which naturally involves a certain probability of failure.
Thus, via the C2 link, the PIC can control the flight of the, at least temporarily, unmanned aircraft or spacecraft using the flight control system, the drive system or the undercarriage system, can monitor and control the danger avoidance systems (DAA, detect and avoid) of the aircraft or spacecraft, and can assist, for example, with functions such as what is referred to as a “handover” between supervisory authorities or a plurality of what are referred to as remote pilot stations (RPS) during the flight procedure or with the recording of flight data. Furthermore, flight parameters and warnings, for example concerning the electrics, hydraulics, avionics, air conditioning system, engine, structure, weather radar of the control device of the RPA, can be monitored and transmitted to the absent pilot. Finally, it is also possible to use the at least temporarily unmanned aircraft or spacecraft as what is referred to as a relay for a further aircraft or spacecraft or also for another at least temporarily unmanned vehicle on the ground.
The functions of speech transmission and/or data transmission between the aircraft or spacecraft and the pilot, a control center or another pilot are provided by the C2 link. Functions of this type, for example when linking a plurality of RPS, are provided, for example, by commercial telecommunications network providers which provide the C2 link, in which case it is quite possible for the quality of the link itself and of the service (QoS) to vary. If there is no line of sight between a C2 transmission station and the aircraft or spacecraft, it may be necessary to revert to satellite links for transmissions.